Interstitial insertion of catheters to apply therapeutic radiation and hyperthermia is commonplace. Several miniature microwave antenna designs are known. Conventional antenna designs are typically 1 to 2 mm in diameter and 5 to 7 mm in length and are operated at frequencies of from about 300 MHz up to about 2450 MHz.
Locally induced microwave hyperthermia for cancer therapy permits flexibility in treatment procedures for tumors of irregular volume and for tumors located deep within the body. Production of adequate thermal field distribution in superficial, accessible and deep-seated tumors is an important consideration. Limited depth of energy penetration has restricted the use of prior art antennas primarily to the heating of well localized tumors extending to depths of up to a few centimeters. Tumors in hollow viscera or cavities such as the oesophagus, cervix and prostate are amendable to treatment with intracavitary hyperthermia techniques. Interstitial hyperthermia techniques are employed for accessible tumors of large volume. A major limitation of prior art interstitial devices is maximization of thermal energy along the sides rather than at the tip of the applicator.
One prior art approach to enhancing the heating at the tip of the applicator is described in Lin, et al., Int. J. Hyperthermia, 3:37-47 (1987). The antenna described operates at 2450 MHz.
A 915 MHz applicator having a diameter in excess of 1 cm and hence too large for use in the treatment of nasopharyngeal cancer is described in Abstract Ce-9, p. 43, "Abstracts of Papers for the Thirty-Sixth Annual Meeting of the Radiation Research Society, Eighth Annual Meeting of the North American Hyperthermia Group", Philadelphia, Pa., Apr. 16-21, 1988, and was shown at that meeting.